[TAP] sync vs async - time outs

[Gerard]

Dear Dave
> > Guy wrote:
> > > However, I see no reason why a TAP installation that 
> always operates 
> > > quickly has to have the asynchronous mode. I would be 
> happy for the 
> > > asynchronous interfaces to be made optional; but only on the 
> > > understanding that most TAP services will need them and that 
> > > software authors be prepared to add them when that need 
> is discovered.
> > >  
> > I support this, but think we should let a service specify what they 
> > think is "quickly".
> 
> In practice 'quickly' is controlled by the settings on all 
> the various network routers, switches and proxies handling 
> the connection between client and server.
> A database server may take 25 seconds to think about a 
> complex query, but if one of the network switches handling 
> the connection thinks 20 seconds is an appropriate timeout, 
> the response will never arrive.
> 
Point well taken.
This is indeed the main problem I have encountered.
Queries that require a complete scan through a table to be completed before
obtaining any result, for example
when calculating aggregate quantities, have timed out because of session
timout settings on proxy and web servers.

There clearly is a place for /async.
Another motiviation for implementing it is because it makes it
easier/possible to queue jobs.
It seems that "I/O concurrency" scales much worse than linear. 
Being able to queue requests so that at most a few access the same disk at
the same time seems better for performance.

Thanks
Gerard